Throttle hang when grabbing gears..

R

RedRotors

New member
Joined
Jan 26, 2009
Messages
6
Hi ,

I have my 03 since a while and I'm still looking at this issue. It's worst when the engine is cold. Tuned or not, same issue.

When raising rpm to shift gear, let's say 2000rpm, when I lift my foot from
the throttle, rpm stay at 1900-2000 for about a second and half then slowly drop.

Anyone has an idea ?

cheers,
Marc
 
A lot of the CR 5.9's do it. My 07 with Smarty TNT-R did it pretty bad. Tolerable if you know it's there when you drive
 
Looks like a common problem, but I'm more after what can cause this.. For instance, VW has a CR engine, and I'm not experience this problem at all.. So imo it has to do with ECM... but maybe someone can chime in with some details...
 
I would have initially agreed rail hang, but he said it is doing it stock without the smarty as well?

Marc just to clarify if you put the stock tune in and take the smarty out, it is still having the throttle hang?
 
RedRotors said:
Looks like a common problem, but I'm more after what can cause this.. For instance, VW has a CR engine, and I'm not experience this problem at all.. So imo it has to do with ECM... but maybe someone can chime in with some details...
Click to expand...

Duramax is a CR as well and doesn't seem to have this problem either. It was just called "rail hang" for forever. I believe it's something written into the ECM from the factory that box tuners amplified. I'd almost bet it's a safety kinda built into the ECM where it sees substantial rail pressure, and when people just completely let off the throttle, it steps down the injectors vs just going straight to 0% injection (idle injection) with a bunch of rail pressure.

Totally guessing there but it wouldn't surprise me
 
Cummins_Bred said:
Duramax is a CR as well and doesn't seem to have this problem either. It was just called "rail hang" for forever. I believe it's something written into the ECM from the factory that box tuners amplified. I'd almost bet it's a safety kinda built into the ECM where it sees substantial rail pressure, and when people just completely let off the throttle, it steps down the injectors vs just going straight to 0% injection (idle injection) with a bunch of rail pressure.

Totally guessing there but it wouldn't surprise me
Click to expand...

Not a whole lot of 6 speed dirtys out there either where it'll affect them. In an auto it's really not the end of the world if it hangs a bit when you let out


Sent from my iPhone using Tapatalk - now Free
 
Being this is an 03 this is pure speculation, but if they are tuned any thing like the 06-07s it is in the fuel pressure map. The smarty amplifies this by over shooting the rail pressure then the limiter has to pull it back down. When smoothing, and matching the pressure vs MM3 in the main injection event it makes all of the difference, at least it does on my 07 manual truck.
 
My auto was noticeable, but very tolerable. Manual should be even easier, just push in the clutch
 
Cummins_Bred said:
My auto was noticeable, but very tolerable. Manual should be even easier, just push in the clutch
Click to expand...

Roommate from college had it bad in a 6 speed 03 and between shift it would hang bad when he pushed the pedal in. Had a predator and power puck on his truck so idk.


Sent from my iPhone using Tapatalk - now Free
 
dvst8r said:
I would have initially agreed rail hang, but he said it is doing it stock without the smarty as well?

Marc just to clarify if you put the stock tune in and take the smarty out, it is still having the throttle hang?
Click to expand...

I tried to put back the stock tune and same thing.. I just took a ride and watched at my RP gauge while shifting, and as soon as i lift my foot the RP drop to 7-8k ( while being at 13k at 2000rpm ), but the RPM still hang..
 
Is this at WOT or at part throttle, if it is part throttle how far down on the petal before lifting to shift?
 
Could also be a program in the ecm to help with the holy going from idle back to high rpm.
 
30 RUM said:
Is this at WOT or at part throttle, if it is part throttle how far down on the petal before lifting to shift?
Click to expand...

it's part throttle, maybe 25-35%, at WOT, its worst.. I read somewhere that
newer truck had an ecm update and it fixed the problem.. so that let me think it's a lazy oem mapping inside..
 
When I see the many threads like this one it has me wondering.....

How many owners who step up their fuel delivery systems(i.e-Injectors,Lift Pumps &Tuners) actually place ANY thought into the returning fuel to the tank and its line(s).

With the larger lift pumps & big lines,injectors and the tuners ramp up rates and a hard romp on the loud pedal IMO rail hang wouldn't be as much of a issue if the owners put any thought into the straw sized factory return line.Those lines create the backlog of pressure that resonates into the entire fuel system when an abrupt lift of the throttle happens.Ever wonder how many owners who crack an injector ever addressed their return systems and tank vents?...Just My .02 worth.......Andy
 
I use the factory return and since I'm using a sump, the factory supply is now a return line specifically for the Dmax top pump while the factor return does the factory pump, RV and head return.
 
You must log in or register to reply here.
Back
Top